What stain is used for carboxylated acid mucopolysaccharides?

• A. Alcian Blue 2.5 and colloidal iron
• B. Alcian Blue 1.0
• C. Congo Red
• D. PAS

Answer: (A)

Acidic mucopolysaccharides that contain carboxyl groups are detected by Alcian Blue because the dye is positively charged and binds to the negatively charged groups on these mucins. When used at a pH of 2.5, Alcian Blue stains both sulfated and carboxylated mucopolysaccharides, making carboxylated ones visible. Adding colloidal iron intensifies this interaction, producing a stronger, more easily observed blue stain in tissue sections. The pH 1.0 variant would miss carboxylated mucins, staining only sulfated ones, while Congo Red and PAS stain other substances (amyloid and neutral carbohydrates, respectively) and don’t specifically highlight carboxylated acid mucopolysaccharides.